So called unitized seals can be installed in the annular space between a pair of relatively rotatable members, such as bearing races. A pair of nested, coaxial metal casings, one press fit onto each bearing race, enclose internal rubbing seals. Many examples of unitized seals can be found in the issued U.S. patents. Some designs have only one seal, which is attached to one casing and rides on the other, as in commonly assigned U.S. Pat. No. 4,572,516 to Symons et al. Others have more than one seal, all attached to one casing and riding on the other casing, as in commonly assigned U.S. Pat. No. 4,497,495 to Christiansen or U.S. Pat. No. 4,958,942 to Shimizu. Yet others have one seal on each casing, each of which rides on the other casing, as in U.S. Pat. No. 4,185,838 to Danner. The aforementioned patents all show designs in which the seals are integrally molded to one or more of the stamped casings, a process that can be somewhat difficult to control due to complexity in the seal shapes or variations in the metal stampings. Another shortcoming of the various designs is that there is typically no provision for retaining the casings together against axial separation, prior to installation, apart from separately rolling or crimping over an edge of one of the metal casings to overlap the other. This requires an additional manufacturing step subsequent to nesting the casings together.
A newer type of unitized seal eliminates the seal molding step by using sealing disks cut from flat sheets of polytetrafluoroethylene (PTFE) material and separately bonding or otherwise attaching them to one casing in an orientation where they make sealing contact with the other casing. Much lower seal torque or friction is possible with PFTE disks, because of the slippery nature of the material. Generally, such seal designs have the same general configuration as equivalent molded designs, so the same problem of preinstallation casing separation is faced. An example may be seen in U.S. Pat. No. 5,024,364 to Nash et al. All the embodiments incorporate two disks of PFTE, one fixed to each casing, each of which makes one sealing contact line with the opposite casing. In the FIG. 4 embodiment, there is no structure to directly block axial separation of the two casings. In the FIG. 3 embodiment, edges of the casings are crimped over at (56) and (58), so as to resist axial separation of the casings by blocking the edges of the disks. However, as shown, the casing crimped edges (56) and (58 ) are preformed, which means that, as the casings are pushed together, the edges of the disks are dragged across the casing edge and flexed away to a great extent. Should the disk flex to such a degree that it takes on a permanent set and does not make good sealing contact, there is no easy way to correct the problem.
A problem faced by both types of seals, integrally molded and PFTE, is the inevitable running eccentricity that bearing races are subject to, which continually widens and narrows the annular space between them. This means that the seal disks have to be given enough interference with the casing surfaces on which they ride to assure that sealing contact is maintained when the annular space widens. One approach, as shown in FIG. 4 of the Nash patent, is to cut a disk so large that it has a very large area of contact with the casing surface on which it rides. Sealing contact is assured, but the extra seal interference does increase seal friction, in spite of the slippery nature of the the seal material. Providing less interference between the edge of the disk and the casing surface on which it rides, as shown in FIG. 6 of the same patent, produces much less running friction. However, a narrow wedge shape is thereby created between the edge of the disk and the casing surface that it rides on, and the constant widening and narrowing of the annular space between the bearing races has the same effect on the wedge. This can create a pumping action that acts to continually drive material away from the disk edge. The edge of the disk can either be bent in a closed orientation, with the wedge facing away from the space that it is sealing, or in an open orientation, with the wedge facing toward the space that it is sealing. The closed orientation is preferred, because it is harder for materials to get under the edge of such a disk. But once material does get under, its migration is assisted by the pumping action. Another problem is disk edge damage that can potentially occur during shipping and handling if the casings are displaced radially far enough to pinch the disks.